Beam indexing is not a new technology; however, neither has it been successfully implemented to the point of commercial feasibility. Beam indexing systems of a type employing both a pilot beam and a writing beam have been exploited in the prior art (a method most widely publicized is the Philco "Apple Tube" which was developed and demonstrated in the mid 1950's). Briefly, the Philco Apple Tube is designed with a single gun having two beams, a writing beam and a pilot beam. Phosphor is deposited in sequential red, green and blue stripes with black, non-luminescent material the same width as the phosphor stripes laid between each color stripe to serve as a guard band. Each red stripe is backed with a stripe of secondary emitting material running the height of the screen. The pilot beam striking the secondary emitting stripes produces the sense signal, which is fed back to servo the deflection circuitry. Reference concerning description of the Philco Apple Tube beam indexing system is made to the following: "Television Receiver Uses One Gun Color CRT", electronics, June, 1956, Pages 151-153; "A New Beam Indexing Color Television Display System," R. G. Clapp, et al, Proceedings, I.R.E., Vol. 44, September, 1956, Pages 1108-1114; "A Beam Indexing Color Picture Tube--The Apple Tube", G. F. Barnett, et al, Proceedings I.R.E., Vol. 44, September, 1956, Pages 1115-1119; "Current Status of Apple Receiver Circuits and Components", L. A. Bloomsburg, et al, Proceedings I.R.E., Vol. 44, September, 1956, Pages 1120-1124. The Philco Apple Tube type of beam indexing system might best be described as a continuous beam indexing system in that such a system continually tries to correct for beam target errors throughout the scan.
Other types of single beam indexing systems operating on a continuous basis have been widely exploited in the art and generally comprise a single beam cathode ray tube employing special indexing stripes on the cathode ray tube face in addition to the red, green and blue stripes, the special indexing stripes being capable of emitting non-visible radiation from emitting substances capable of producing ultra-violet, x-ray, infrared, etc., emissions upon beam impingement thereon. These types of systems, again as in the Apple Tube indexing system, operate on a continuous basis as the beam is swept over the face of the tube, and are typified by teachings of the following patents: Chen, U.S. Pat. No. 3,732,359; Keizer, U.S. Pat. No. 2,809,233; Keizer U.S. Pat. No. 2,883,451; Sziklai U.S. Pat. No. 2,892,020; Schwartz U.S. Pat. No. 3,469,024; Thompson U.S. Pat. No. 3,875,450; Archakov U.S. Pat. No. 3,881,182; Fredendall U.S. Pat. No. 2,933,554; Chatten U.S. Pat. No. 3,041,391; Goodman U.S. Pat. No. 3,277,235; Goodman U.S. Pat. No. 3,691,424; Fumomoto U.S. Pat. No. 4,003,082; and Sunstein U.S. Pat. No. 3,893,165.
The above prior art teachings employ, to varying degrees of complexity, a special cathode ray tube face with indexing stripes geometrically associated with green, red and blue stripes and with means to detect nonvisible radiation from the indexing stripes for the purpose of effecting a beam indexing function. Again, the teachings in these references attempt to operate on a continuous basis as the beam is swept across the face of the tube.
Since beam indexing infers knowing where the beam is at any point in time, all such systems include a means for including linearity corrections as concerns the beam deflection. Linearity correction circuits employed for correcting pincushion distortion, for example, in the cathode ray tube have been highly exploited, as exampled in Eggert U.S. Pat. No. 3,487,164; Williams U.S. Pat. No. 3,517,252, Kapers U.S. Pat. No. 3,758,825; and Gray U.S. Pat. No. 3,422,306. These teachings relate to linearity correction due to known distortions encountered in a cathode ray tube deflection system where the radius between the gun and the tube face is less than that of the curvature of the tube face, per se, resulting in well known pincushion distortion.
Certain other known prior art techniques relating to linearity correction employ "sampling" techniques wherein the correction is determined for a particular point on the screen and this error, or correction, is extrapolated over a predetermined portion of each scan or over a predetermined area of the viewing screen. Systems of this type are exampled in Manber U.S. Pat. No. 3,740,608 and McCarthy U.S. Pat. No. 3,852,640.
The more recent teachings of Manber U.S. Pat. No. 3,740,608 and Horvath U.S. Pat. No. 3,714,496, employ storage of digital correction values associated with particular regions of the tube, and these correction values are subsequently called out to modify beam deflection signals. In these instances, however, the correction values are premeasured, as by microscopic comparison between template defined positions and actual beam positions.
Known prior art teachings are thus directed to (1) linearity correction of cathode ray tube deflection circuitries to overcome pincushion distortion (2) to the use of cathode ray tubes without shadow mask and employing continuous beam indexing systems utilizing special indexing stripes capable of emitting a nonvisible radiation which may be detected and utilized to effect a controlled relationship between beam position on the tube face and color phosphor depositions thereon (3) to such continuous beam indexing systems employing a writing beam and a pilot beam as well as to such systems employing a single beam and (4) means for storing correction values as a function of beam position for subsequent readout for beam position correction during a sweep sequence where the correction values are premeasured for a particular tube and placed in storage for readout and correction.